The Response Of Leaf Morphology And Physiological Characteristics To Elevation Gradient In Abies Georgei Var. Smithii

Abies georgei var. smithi is mainly occurred at the elevations above 1500m. Whereas the relationships between growing procedure of this tree species along altitudinal gradient and the environmental conditions are unclear. In our present study, leaf ecophysiological traits, which were closely related to the environmental conditions, were measured at an altitudinal range from 2900 to 4300m to study adaptation mechanisms of the Abies georgei var. smithi to varied environments. By measuring stomatal properties, biomass, nitrogen concentration per mass and stable isotope composition of leaves at 15 altitudinal gradient, we were aimed to address the following questions:(1) How leaf traits of Abies georgei var. smithi varied with altitudinal gradients; (2) how leaf chemical elements including nitrogen concentration per mass and stable isotope composition in the leaves of Abies georgei var. smithi varied with altitudinal gradients and tried to explain the mechanisms that maintained balanced carbon metabolism; (3) to find the relationships between stable carbon isotope composition and leaf nitrogen concentration per mass and specific leaf weight (SLW). Results are:1. Leaves wide showed significant orders along with altitudinal gradient, which indicated a relatively conservative property in leaf morphology of the Abies georgei var. smithi and the influence of environment on this property was weak. The leave length and area had curvilinear correlations with variance in altitudes, probably due to decreases in temperature and increases in relative humidity. Leaves length and area increased with altitude at range of 2900-3800m, which might be correlated to a special a property of this tree, which often favors to cold and wet condition. However, the leaves length and area decreased with altitudinal increases at 3800-4300m. The reason for this might be that the low soil temperature restricts plant root to absorb soil water and gradually enlarges water intimidation. In addition, another reason might be that, at high altitudinal site, decreased leaves length and area are just apparent adaptation property of leaves to the cold and dry climatic condition.2. Leaf biomass (dry weight of leaf and SLW) increased with increasing altitudesl at range of 2900-3800m, but decreased with increasing altitudes at range of 3800-4300m. These indicate that the capability of CO2 assimilation in leaves increases gradually below 3800m, which further promotes dry material accumulation of leaves. While above 3800m, due to the decreased CO2 and increased ultraviolet radiation,decreases in leaf biomass production were detected.3. By studyingδ13C in leaves of Abies georgei var. smithi, we found that the variations ofδ13C were small and the mean values were low. In addition, there were no linear relationship betweenδ13C of leaves and altitudinal gradient and the variation were not regular. The irregular correlation betweenδ13C of Abies georgei var. smithi leaves and altitude might be results of joint effect of interspecies competition between different tree species at Sejila mountain and temperature as well as precipitation etc.4. Except were there abnormal variation at 3800m of altitude, the insignificant variation in nitrogen concentration per mass(Nmass)of specific leaf weight at other altitudinal gradients indicated that Nmass of leaf and dry material of leaves do not vary with altitudes. The abnormal increasing in Nmass and dry material content of leaves at 3800m were significantly effected by specific microclimatic condition. Nitrogen concentration of specific leaf area had curvilinear correlation with altitudinal gradients. At the range of 2900-3800m, the nitrogen concentration of specific leaf area decreased significantly with increases of altitude which indicated that below 3800m the maximum photosynthetic capability of the Abies georgei var. smithi increased gradually with increasing altitudes. Above 3800m, the regional temperature falls significantly and the soil temperature decreases significantly as well. The relatively low soil temperature restricts Abies georgei var. smithi roots to uptake soil water and further produce water intimidation. In addition, UV-B radiation increases with increasing altitudes, the photosynthetic capability of Abies georgei var. smithi was weak.5.Analizing nitrogen content of specific leaf area and SLW indicate that there is a positive correlation between Narea and LMA(R2=0.85794)because Abies georgei var. smithi had made an evolutionary adaptation to its environment and allocate much more nitrogen to its photosynthetic organ and causes the biomass of leaf per unit of area increases with the increase of nitrogen concentration of leaves.